Methanol fueled turbocharged diesel cycle internal combustion engine

ABSTRACT

The combination of an intake air supply system with an internal combustion engine having a charge air cooler, a cylinder charging air intake and an exhaust discharge is provided. The intake air supply system includes a Roots-type positive displacement blower having inlet and outlet means and an exhaust gas driven turbo-compressor connected in series with the blower. The intake air supply system further includes a bypass passage connecting the blower inlet and outlet and a valve in the bypass passage to control the flow of fluid through the bypass. The valve is operative to open and close the bypass passage in response to engine operating parameters and to modulate the flow area of the passage in response to the same engine operating parameters so as to infinitely vary the flow area between the open and closed positions of the valve. The valve is modulated to operatively maintain the bypass passage at least partially open at engine idle, whereby the valve means permits bypass flow to recirculate air flow from the blower outlet to the inlet to reduce or limit the engine power absorbed by the blower or to conduct additional air flow around the blower directly from the turbo-compressor to the engine intake to avoid the restriction of the blower to increased charging air flow. A single valve means thus provides a dual function capability.

TECHNICAL FIELD

The present invention is related to methanol fueled internal combustionengines, and, more particularly, to two-cycle compression-ignitionengines.

BACKGROUND ART

Conventional compression-ignition (CI) engines in use today forvehicular and other industrial uses are fueled by a high grade fuel oilknown as "No. 1 or No. 2 grade" and as "diesel fuel." It is a petroleumbased fuel, high in hydrocarbons, has good lubricity characteristicswhich assists in lubricating the injectors and other moving partsexposed to the fuel prior to its being introduced into the combustionchamber, and is ignitable with or without the assist of a glow plug atrelatively low geometric compression ratios ranging up to as much as19:1.

However, with the advent of concern over reducing nitrogen oxides,particulates, highly reactive hydrocarbons and other combustionby-product emissions into the environment, there has been increaseddesign effort in maximizing the emission characteristics of this fuel.Some have been cost effective (i.e. higher performance and greaterthermal efficiencies), while others have not (i.e. the addition ofparticulate traps).

Coincident with these emission concerns, has been the concern ofpetroleum-based fuel shortages and the need for alternative fuelsources. Among the alternatives considered are low cetane liquid fuels,such as methanol and ethanol, as well as low cetane gases, such asnatural gas.

Methanol is a particularly attractive fuel alternative since it is aliquid fuel, therefore, compatible with known liquid fuel systems.Additionally, methanol is a by-product of natural gas, an abundantenergy resource. The special properties of methanol, however, requiremajor engineering changes in engine design and the design of the airsupply and fuel systems, just to name a few.

U.S. Pat. No. 4,539,948, issued to Toepel and assigned to the assigneeof the present invention, describes an internal combustion engine of thetwo-cycle compression-ignition type for handling methanol fuels wherebythe scavenging, i.e. clearing the exhaust gases from the combustionchamber immediately following combustion, is controlled so as to allow acertain amount of hot residual gases to remain in the combustion chamberto support and promote the auto-ignition of the methanol fuel during thenext power cycle.

U.S. Pat. No. 4,502,283, issued to Wandel and assigned to the assigneeof the present invention, discloses an automatically actuated valvingarrangement for routing the engine blower discharge air through a bypassof the combustion chamber-cylinder liner air box upon the sensing of aparticular air pressure. Thus, the full air delivery capacity of theblower is either fully utilized in assisting the combustion process, orcompletely removed therefrom.

U.S. Pat. No. 4,738,110, issued to Tateno, discloses a diesel engineequipped with a mechanically driven charger. The engine comprises anexhaust-gas driven turbocharger, a mechanically driven chargerpositioned in the engine intake passage, connection control means forcontrolling the mechanical connection between the mechanically drivencharger and the engine, a bypass passage connected to the intake passagedownstream of the charger and valve means controlling a bypass air flowwithin the bypass passage. The engine further includes control means forcontrolling the connection control means and the valve means in responseto output signals from a plurality of detecting means for detectingstarting and operation of the engine.

U.S. Pat. No. 4,394,812, issued to Mezger, discloses a superchargedinternal combustion engine for motor vehicles. The engine has an exhaustgas turbine driven supercharging blower, exhaust gas bypass forregulating the exhaust gas turbine by diverting exhaust gases around theturbine and a blow-off valve control charging air bypass for circulatingcharging air supplied from the blower. The engine also has a secondcharging air bypass for circulating a portion of the air supplied by theblower therearound in response to at least one engine operatingparameter so as to provide protection against excess charging pressure.The at least one engine parameter includes engine speed and/or chargepressure. A solenoid valve controlled by a safety switch may be utilizedto control opening of the second bypass.

Despite these prior efforts, until the present invention, there was notwo-cycle CI engine in use, fueled solely by methanol or any other lowcetane liquid fuel. Despite the knowledge represented by theabove-mentioned prior art, and other expertise in the field, there weremany problems to be overcome for the successful long-range CI enginehaving satisfactory durability and performance. The present invention isdirected to those major remaining concerns.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aturbocharged and aftercooled blower-assisted two strokecombustion-ignition engine having the means to automatically modulatethe amount of input air admitted to the combustion air box from a blowerduring engine operation throughout all engine load conditions and overthe entire speed range of the engine.

The invention further contemplates the aforementioned objective wherebythe primary feedback parameters upon which the modulation is based areturbocharger boost pressure, throttle position, and engine speed and thesecondary feedback parameters may include engine coolant temperature andbarometric pressure.

The invention further contemplates the above mentioned objective beingused as a means of maintaining within the combustion chamber, from onecombustion cycle to the next, sufficient high temperature residualexhaust gases capable of absorbing the cooling down effect of therelatively large volume of methanol fuel required to produce the powerequivalent to the diesel-fueled engine while ensuring auto ignition ofthe compressed fuel air charge at all operating speeds and loadconditions.

The invention further contemplates an automatically continuouslymodulated bypass blower control system in combination with an ultra highgeometric compression ratio in the order of 23:1 which will assure autoignition of the fuel air mixture compressed charge at all engine speedsand load conditions and limit the use of glow plug ignition enhancementto a duty cycle limited to start-up and warm-up and preclude the needfor fuel-based ignition enhancers.

In carrying out the above objects, the combination of an intake airsupply system with an internal combustion engine having a charge aircooler, a cylinder charging air intake and an exhaust discharge isprovided. The intake air supply system includes an engine drivenpositive displacement blower having inlet and outlet means and anexhaust gas driven turbo-compressor connected in series. The compressordischarges to the blower inlet and the blower outlet discharges to thecharge air cooler and to the engine air intake. The intake air supplysystem further includes a bypass passage connecting the blower inlet andoutlet and a control valve means in the bypass passage to control theflow of fluid through the bypass. The control valve means is operativeto fully open and fully close the bypass passage in response tocontinually sensed engine operating parameters and to modulate the flowarea of the passage in response to the same engine operating parametersso as to infinitely vary the flow area between the fully open and fullyclosed positions of the control valve means. The control valve means ismodulated to operatively maintain the bypass passage at least partiallyopen at engine idle, whereby the control valve means permits bypass floweither (a) to recirculate air flow from the blower outlet to the inletto reduce or limit the engine power absorbed by the blower or (b) toconduct additional air flow around the blower directly from theturbo-compressor to the engine intake to avoid the restriction of theblower to increased charging air flow. A single control valve means thusprovides a dual function capability.

The above objects and other objects, features and advantages of thepresent invention are readily appreciated by one of ordinary skill inthe art from the following detailed description of the best mode forcarrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1d are pictorial representations of the various operatingcycles of a two-cycle compression-ignition engine in accordance with aconventional practice and being a part of the prior art;

FIG. 2 is a transverse cross-sectional view of a two-cycle diesel engineadapted for methanol operation in accordance with the invention;

FIG. 3 is a exploded perspective view of the bypass blower inlethousing, or "air horn," as it is conventionally known, in accordancewith the present invention;

FIG. 4 is a block diagram of the hardware associated with the bypassblower control system according to the present invention;

FIG. 5a is a block diagram of the fuel control strategy for use with thepresent invention;

FIG. 5b is a block diagram of the bypass blower control system for usewith the present invention;

FIG. 6 is a flowchart illustrating the method of controlling the bypassblower of the present invention; and

FIG. 7 is a graphic illustration of the relationship between scavengeratio, scavenge efficiency and trapping efficiency in accordance withthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As is known, a methanol fueled two-cycle compression-ignition (CI)engine is an internal combustion engine in which the energy of methanolis converted into work. In this methanol engine, air alone is compressedin the cylinder. After the air is compressed, a metered amount of fuelis injected into the cylinder and ignition is accomplished by the heatof compression. Glow plugs are used to aid starting and engine warm-up.

The Two-Cycle Principal

Referring now to FIGS. 1a-1d, there is shown a timed sequence operationof a turbocharged and aftercooled two-cycle engine During operation ofthe engine, intake and exhaust occurs during part of the compression andpower strokes.

Intake air is boosted in pressure and temperature when passing throughthe turbocharger compressor and on to the blower 37, which is used toforce air through an aftercooler and into the cylinders 16, expellingthe exhaust gases and providing fresh air for combustion. The cylinderliner contains a row of ports 30 disposed therein so as to be above thepiston 17 when the piston is at the bottom of its stroke. These portsadmit air from the airbox into the cylinder as soon as the pistonuncovers them during its downward stroke.

The air flows generally toward the exhaust valves and removes most ofthe burned exhaust gases from the previous stroke, thereby leaving thecylinder with a mixture of fresh air and burned exhaust gases as thepiston again covers the ports 30 during its upward movement, as bestshown in FIG. 1a. This portion of the piston stroke is commonly referredto as the scavenging portion.

It is important to note, however, that some quantity of burned gaseswill remain in the cylinder and add heat to the next charge of incomingair. While this may seem, at first, to be inefficient, it is necessaryfor proper engine operation on methanol fuel. It is also important tonote the heating or cooling effect of the aftercooler 52 immediatelydownstream of the blower 37. High load performance and durability of theengine is enhanced by the low temperature charge air that leaves theaftercooler. Conversely, at light loads, the heating effect of theaftercooler is important to maintaining auto-ignition of the methanolfuel.

As the piston 17 continues on its upward stroke, the exhaust valvesclose and the mixture is compressed, creating heat, as best shown inFIG. 1b. This portion of the piston stroke is commonly referred to asthe compression portion.

Shortly before the piston reaches "top dead center," a metered amount offuel is preferably injected into the cylinder 16 by the fuel injector36. The heat generated during compression ignites the fuel, causingcombustion and forcing the piston downward so as to create power, asbest shown in FIG. 1c. This portion of the piston stroke is commonlyreferred to as the power portion. As the piston moves downward on thepower stroke, the combustion continues until all the fuel injected intothe cylinder 16 has been burned.

When the piston is about halfway down, the exhaust valves are opened soas to allow the burned gases to escape into the exhaust manifold.Shortly thereafter, the piston 17 uncovers the inlet ports 30 and freshair from the blower 37 is again admitted into the cylinder 16, as bestshown in FIG. 1d. This portion of the piston stroke is commonly referredto as the exhaust portion of the stroke.

As is known, the entire combustion cycle as described above is completedin each cylinder for each revolution of the crankshaft, or, in twostrokes. Thus, the engine is a "two-stroke cycle" engine.

The Invention

Referring now to FIG. 2, there is shown an engine generally indicated byreference numeral 10, of the multi-cylinder two-cycle diesel type.Engine 10 includes a cast cylinder block and crankcase 12 having a pairof cylinder banks 13 and 14 arranged in a "V". Each cylinder bank isprovided with a plurality of longitudinally aligned cylinders 16. Aplurality of pistons 17 are reciprocally disposed, one in each cylinder,and connect through connecting rods 18 with a crankshaft 20, which isrotatably supported in conventional fashion in the lower crankcaseportion of the block 12.

The cylinder block further defines upper and lower coolant jackets 21and 22 which respectively extend around the upper and lower portions ofthe cylinders and are interconnected for coolant flow therebetween. Thecentral portion of the lower coolant jacket 22 extends between thecylinder banks to form a longitudinally extending central chamber 24,closed by an upper wall 25. The cylinder block also defines an inlet airchamber, or air box 26, outer portions of which extend around thecenters of each of the cylinders between the upper and lower coolantjackets. An open central plenum 28 extends above wall 25 and connectsthe air box outer portions to an opening 29 in the top of the cylinderblock between the two cylinder banks. Ports 30 are provided around thecentral portions of the cylinders to permit air to flow into thecylinders from the air box 26 as controlled by the motion of the pistons17, as described above.

Each cylinder bank is preferably provided with a cylinder head 32mounted to close the upper ends of the cylinders of its respective bankand containing a plurality of exhaust valves 33, exhaust passages 34controlled by the valves, and a fuel injector 36 for each cylinder.Actuation of the valves and injectors is conventionally controlled byvalve gear operated in timed relation with the engine crankshaft.

In the preferred embodiment, a glow plug 60 is mounted in each of theengine cylinder heads 32. The glow plugs are of conventionalconstruction and include a tip portion 66 which extends into each enginecylinder 16 within the bowl (not specifically illustrated) formed in thehead of its associated piston 17 (at its top dead center position) andnear the tip 69 of the associated fuel injector 36. The glow plugs 60are connected through an electrical contact 70 with conventional means(not specifically illustrated) for energizing and controlling operationof the glow plugs as required.

A Roots-type positive displacement blower 37, sometimes referred to asthe bypass blower, is preferably centrally mounted on the cylinder blockbetween the engine cylinder heads. Blower 37 has an inlet opening 38 inthe upper portion of its housing, a plurality of lobed impellers 39working in an enlarged central portion, and an outlet opening 40 in thelower portion of its housing and with the aftercooler 52 positionedwithin the air box inlet opening 29 of the cylinder block.

With continuing reference to FIG. 2, a turbocharger 41 is shown to bemounted on the engine 10 in a known fashion and includes a dynamiccompressor portion 42 and a turbine portion 44. The compressor portion42 has an air inlet (not specifically illustrated) adapted to beconnected with an air source and an air outlet 45 connected by an airhorn 46 with the inlet 38 of the blower 37. The turbine portion 44includes an outlet (not specifically illustrated) and an inlet 48connected by suitable conduit with exhaust manifolds 50 mounted on theengine cylinder heads and connecting with the exhaust passages 34thereof.

Aftercooler 52 is received within the central plenum 28 of the engineair box. The aftercooler 52 is preferably supported within the cylinderblock by a flange 56 secured within a recess 57 provided around the edgeof the air box inlet opening 29. The aftercooler directs air deliveredby the blower 37 through vertical passages (not specificallyillustrated) in heat exchange relation to the engine coolant anddirectly into the central plenum 28 of the air box 26.

The foregoing is further described in U.S. Pat. No. 4,539,948, thesubject matter of which is herein incorporated by reference.

In the preferred embodiment, the Roots blower 37 is provided with aplurality of bypass passages 58 that extend within the blower housingaround respective sides of the central portion containing the impellers39. The passages 58 thus provide an alternate flow path around theimpellers from the air horn 46 leading from the turbocharger compressorto the aftercooler 52.

As best shown in FIG. 3, a blade-type control valve or bypass valve 54is generally located at the entrance of each passage 58 within the airhorn 46 so as to control air flow through each bypass passage 58. Eachvalve 54 is preferably affixed to a common control shaft 62 rotatablysupported by the air inlet housing or air horn 46. A rocker arm 64serves to rotate the shaft 62 such that the passages 58 are closed oropened by the oscillating movement of the respective control valve 54.

Referring to FIG. 4, it can be seen that the bypass actuator 74 ispneumatically actuated. Preferably, the actuator 74 includes a flexiblediaphragm 81 radially outwardly sealed to the housing member 76, so asto divide the actuator 74 generally into two chambers 78 and 80. Apiston stem 82 is affixed to the central portion of the flexiblediaphragm 81. The chamber 80 is open to ambient pressures and thechamber 78 receives air under pressure in varying amounts from solenoidvalve 86, which controls the amount of air flowing from a pressurizedair source, not specifically illustrated, through regulator 88 and airhoses or lines 90 and 92 to the bypass actuator 74.

As best shown in FIG. 3, the piston stem 82 preferably includes aball-in-socket end 84, which is pivotally connected to the valve rockerarm 64. The ball-in-socket end 84 further includes a spring member (notspecifically shown) which operates to constantly urge the piston stem 82in the direction of the housing member 76 and, therefore, the bypassvalves 54 to a position wherein the passages 58 are fully closed.

With continuing reference to FIG. 4, the solenoid valve 86 is preferablycontrolled by an electronic control module (ECM) 100 via line 96. Thus,when the solenoid valve 86 is energized, air enters the actuator 74, thechamber 78 is filled and the flexible diaphragm 81 is urged outward.This in turn moves the piston stem 82 outward from the actuator 74, soas to rotate the rocker arm 64 and, therefore, the bypass valves 54. Theactuator 74 includes a potentiometer 75 for detecting the actualposition of the actuator 74 (i.e. the piston stem 82) and generating afeedback signal which is supplied to the ECM 100 via line 83, therebyproviding accurate feedback bypass blower control.

As shown in FIG. 2, the ECM 100 preferably receives input from aturbocharger compressor outlet pressure sensor 98 located in the outlet45 of the turbocharger 41. This measure of the turbocharger's boost tothe air inlet charging system is, of course, only one of a number ofengine parameters sensed and fed to the ECM 100. The ECM 100 alsoreceives sensory inputs relating to the throttle position and enginespeed from sensors (not specifically illustrated).

In the preferred embodiment, the ECM 100 is a Detroit Diesel ElectronicController (DDEC) II and includes a microprocessor, RAM-type memory,EPROM-type memory and analog-to-digital (A/D) circuitry. As is known,the microprocessor performs calculations, the RAM memory is useful forstoring data and the like, the EPROM is useful for storing the softwarewhich controls engine and bypass blower operation and the A/D circuitryconverts analog signals from sensors into corresponding digital data.

Referring now to FIG. 5a, the ECM 100 controls fuel delivery to theengine 10. Based on throttle position and engine speed, themicroprocessor retrieves a corresponding "requested torque" value from atorque table stored in the EPROM and also retrievesbeginning-of-injection timing data from timing tables stored in theEPROM. Similarly, the microprocessor utilizes engine speed and manifoldpressure data to retrieve a corresponding "allowable torque" from aseparate table also stored in the EPROM. The requested torque and theallowable torque are then compared and the lower of the two is selectedas the "desired torque".

The microprocessor then determines if any governing functions need to beperformed. These governing functions could include idle speed governing,high-speed governing, or the like and modify the desired torque into a"final desired torque", which is stored in the RAM.

The microprocessor then determines the proper pulse width for the fuelinjectors as a function of the final desired torque and the engine speedfrom a conversion table stored in the EPROM. Next, the microprocessorutilizes supplemental injector timing tables and performs outputcompensation based on the individual injector risetime, which is fedbackto the ECM 100.

Turning now to FIG. 5b, there is shown a block diagram of the bypassblower control system. In addition to controlling fuel delivery to theengine as discussed above, the ECM 100 also provides bypass blowercontrol according to the flow chart shown in FIG. 6.

At step 110, a desired air pressure (DESKPA) is preferably retrieved bythe microprocessor from a table stored in the EPROM. The DESKPA value ispreferably a function of the engine speed and the final desired torque.Next, the error in the compressor pressure (ERRKPA) is calculated atstep 112 as follows:

    ERRKPA=DISKPA-ACTKPA

wherein ACTKPA is the actual manifold pressure as sensed by theturbocharger compressor boost sensor 98.

At step 114, the desired position (DESPOS) of the bypass valves 54 aredetermined by the microprocessor as follows:

    DESPOS=BYPGAN*ERRKPA

wherein BYPGAN represents the air pressure to valve position gain.

At step 116, the microprocessor next determines the error in the valveposition (ERRPOS) according to the following equation:

    ERRPOS=DESPOS-BYPPOS

wherein BYPPOS represents the scaled bypass valve position. As notedabove, the bypass valve position is preferably determined utilizingposition feedback.

Having calculated the desired valve position and determined the actualvalve position, the microprocessor next controls the bypass valveposition toward the desired position by adjusting the pulse widthmodulation of the solenoid valve 86 at step 118, as described in greaterdetail above, according to the following equation:

    % PWM.sub.NEW =% PWM.sub.OLD +CLBYPG*[BYPINT*ERRPOS+BYPROP*(ERRPOS-ERRPOS1)]

wherein % PWM_(NEW) represents the adjusted solenoid percent duty cycle(between the upper and lower limits), % PWM_(OLD) represents theprevious solenoid percent duty cycle, CLBYPG represents the valve 54position loop gain, BYPINT represents the valve position integral gain,BYPROP represents the position proportional gain and ERRPOS1 representsthe previous position error.

In accordance with the invention, use of the control strategy discussedabove allows the bypass valve 54 to have an infinite number of positionswithin the passages 58, thereby allowing the ECM 100 to maintain thescavenge ratio, scavenge efficiency and trapping efficiency withinpredetermined limits during engine operation, as described in greaterdetail herein below.

Scavenge ratio is a term commonly used in the art of two-stroke enginesand is defined as the ratio of overall fresh air mass delivered to theideal air mass to fill the cylinder at air box conditions. For a givenengine displacement, scavenge ratio is proportional to overall air flowper cycle, divided by the density of the air in the air box. Scavengeratio combines several parameters, namely air flow, rpm, and air boxtemperature and pressure, into one term which is readily calculated fromdata directly obtainable in a test cell.

Scavenge efficiency can be defined as the ratio of fresh air deliveredand trapped to fresh air delivered and trapped plus residual gases. Inother words, it is important that the fresh incoming air not sweepcompletely the exhaust gases from the combustion chamber, but ratherleave a certain amount of exhaust gases in the combustion chamber sothat the residual heat of these exhaust gases will heat the total airmixture being compressed to a final compression temperature sufficientto withstand the evaporation effects of the fuel being ejected and toautomatically ignite the methanol fuel charge without the assistance ofa glow plug 60 or other ignition enhancements.

Trapping efficiency is also a term commonly used and can be defined asbeing the ratio of the fresh air delivered and trapped to the fresh airdelivered. In accordance with the invention, there is listed in Tables Iand II the typical range and the preferred values for the scavengeratio, scavenge efficiency and trapping efficiency at peak torque andpeak load, respectively.

                  TABLE I                                                         ______________________________________                                        PEAK TORQUE (@ 1200 RPM)                                                                     Range   Preferred                                              ______________________________________                                        Scavenge Ratio   0.7-1.0   0.9                                                Scavenge Efficiency                                                                            70%-90%   87%                                                Trapping Efficiency                                                                            65%-75%   72.5%                                              ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        PEAK LOAD (@ 2100 RPM)                                                                       Range   Preferred                                              ______________________________________                                        Scavenge Ratio   0.4-0.6    0.5                                               Scavenge Efficiency                                                                            60%-80%   75%                                                Trapping Efficiency                                                                            80%-90%   84%                                                ______________________________________                                    

Referring now to FIG. 7, the general relationship between scavengeratio, scavenge efficiency and trapping efficiency are illustrated forthe methanol engine of the preferred embodiment. As shown in FIG. 7, asengine RPM increases, the trapping efficiency generally increases whilethe scavenging efficiency and scavenging ratio generally decrease.

It has been determined that the aforementioned predetermined engineoperating parameters can be produced by utilizing a preferred developedschedule for the degree to which the bypass valves 54 must be openedduring steady state speed and load conditions. This schedule ispresented in Table III below.

                                      TABLE III                                   __________________________________________________________________________        0  150                                                                              300                                                                              450                                                                              600 750                                                                              900                                                                              1050                                                                              1200 - TQ (NM)                                  rpm 0  12.5                                                                             25.0                                                                             37.5                                                                             50.0                                                                              62.5                                                                             75.0                                                                             87.5                                                                              100 - % Max TQ                                  __________________________________________________________________________     600                                                                              40 40 50  70                                                                              100 100                                                                              100                                                                              100 100                                              900                                                                              40 45 50 100                                                                              100 100                                                                              100                                                                              100 100                                             1200                                                                              40 50 70 100                                                                              100 100                                                                              100                                                                              100 100                                             1500                                                                              40 50 70  80                                                                               75  70                                                                               65                                                                               60  60                                             1800                                                                              40 50 65  65                                                                               65  60                                                                               00                                                                               00  00                                             2100                                                                              40 50 60  60                                                                               60  40                                                                               00                                                                               00  00                                             __________________________________________________________________________

The values listed in Table III represent the percent closed angularpositions of the valves 54 in the passage. Thus, "100" represents asubstantially horizontal valve position within the passage, "0"represents a substantially vertical valve position within the passageand "50" represents a generally 45° valve position within the passage.The valve positions are continually monitored, adjusted and optimizedfor performance, durability and transient emission cycles by the ECM 100in accordance with the general formula of:

    VALVE.sub.POS =(Table IV Value-Boost)*Gain

The Table IV value is a control parameter based on steady state testcell conditions, calculated in terms of the Valve_(POS) equation abovewherein boost pressure is measured for various loads throughout theengine's speed range. The "gain" is preferably a fixed value stored inthe ECM 100 and "boost" is measured by the sensor 98 in terms of airpressure at the turbocharger compressor outlet, as described above. Itis a function of engine speed and load throughout position and time. Inthis way, the bypass calibration can be fine-tuned for any specificengine configuration. For the preferred engine, the resulting Table mayappear as follows:

                                      TABLE IV                                    __________________________________________________________________________    Resulting Bypass Table Values                                                 rpm 0  12.5                                                                             25.0                                                                             37.5                                                                             50.0                                                                              62.5                                                                             75.0                                                                             87.5                                                                              100.0 - % Max TQ                                __________________________________________________________________________     600                                                                              119                                                                              119                                                                              126                                                                              140                                                                              161 166                                                                              172                                                                              178 188                                              900                                                                              119                                                                              124                                                                              130                                                                              161                                                                              167 175                                                                              183                                                                              194 207                                             1200                                                                              120                                                                              128                                                                              148                                                                              173                                                                              185 197                                                                              210                                                                              226 249                                             1500                                                                              121                                                                              137                                                                              156                                                                              172                                                                              183 194                                                                              209                                                                              227 251                                             1800                                                                              124                                                                              144                                                                              160                                                                              173                                                                              189 204                                                                              196                                                                              222 254                                             2100                                                                              127                                                                              149                                                                              164                                                                              180                                                                              199 211                                                                              203                                                                              238 279                                             __________________________________________________________________________

Additionally, in accordance with the invention, the geometriccompression ratio is maintained between 20:1 and 25:1. Geometriccompression ratio is defined by the ratio of in-cylinder volume at thebottom-dead-center piston position divided by the in-cylinder volume attop-dead-center piston position. In the preferred embodiment, thegeometric compression ratio is 23:1.

The result of maintaining a high geometric compression ratio whileconstantly monitoring and controlling the bypass blower withinpredetermined parameters so as to maintain the most efficient residualheat effect of the incoming and trapped air is to provide an extremelyefficient, methanol fueled combustion-ignition engine utilizing glowplug ignition only at start-up and warm-up.

It is recommended to read SAE Technical Paper 86110, entitled "DDEC IIAdvanced Electronic Diesel Control" and authored by R. J. Hames, D. L.Hart, G. V. Gillham, S. M. Weisman and B. E. Peitsch, published inconnection with the West Coast International Meeting in Universal city,Calif. on Aug. 4-7, 1986, and hereby incorporated by reference foradditional detail on the DDEC II electronic control module. It is alsorecommended to read SAE Paper No. 831744 entitled "Development ofDetroit Diesel Allison 6-V92TA Methanol Fuel Coach Engine" by R. R.Toepel, J. E. Bennethum, and R. E. Heruth, published in conjunction withthe Fuels and Lubricants Meeting held in San Francisco, Calif., on Oct.31-Nov. 3, 1983 and hereby incorporated by reference.

An extensive discussion of the background, development, features andapplication of an operating embodiment of the invention is described andillustrated in SAE Paper No. 901564 entitled "Development Status of theDetroit Diesel Corporation Methanol Engine" by S. P. Miller and C. L.Savonen, published in conjunction with the International Off-Highway &Power Plant Congress and Exposition in Milwaukee, Wis. on Sep. 10-13,1990. Reference to these papers is recommended for a detailed discussionof the subject matter described herein, and the disclosure of thesepapers are hereby incorporated by reference.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize alternative designs and embodiments for practicing theinvention. It should be understood that the words used are words ofdescription rather than limitation, and that various changes may be madewithout departing from the spirit and scope of the invention asdisclosed. Thus, the above described preferred embodiment is intended tobe illustrative of the invention which may be modified within the scopeof the following appended claims.

What is claimed:
 1. The combination of an intake air supply system withan internal combustion engine having a charge air cooler, a cylindercharging air intake and an exhaust discharge, the intake air supplysystem including:an engine driven positive displacement blower havinginlet and outlet means and an exhaust gas driven turbo-compressorconnected in series whereby the compressor discharges to the blowerinlet and the blower outlet discharges to the charge air cooler and tothe engine air intake; a bypass passage connecting the blower inlet andoutlet; control means including an electronic control module forcalculating a required flow area of said bypass passage in response tocontinually sensed engine operating parameters including engine speed,boost air pressure at the turbo-compressor outlet and operator demand;valve means in the bypass passage to control the flow of fluid throughthe bypass; said valve means being operative to modulate said flow areaas calculated from a fully open position to a fully closed position ofsaid bypass passage thereby infinitely varying the flow area between thefully open and fully closed positions of said valve means; and saidvalve means being modulated to operatively maintain said bypass passageat least partially open at engine idle, whereby said valve means permitsbypass flow, either (a) to recirculate air flow from the blower outletto the inlet to reduce or limit the engine power absorbed by the bloweror (b) to conduct additional air flow around the blower directly fromthe turbo-compressor to the engine intake to avoid the restriction ofthe blower to increased charging air flow, thereby providing a dualfunction capability in a single valve means.
 2. The combination of claim1 wherein said control means includes means for (1) maintaining saidpassage partially closed at engine idle and low load-low speedconditions, (2) maintaining said passage fully closed at low speed-highload conditions and (3) maintaining said passage fully open at highspeed-high load conditions.
 3. The combination of claim 2 wherein saidcontrol means maintains said passage fully closed under heavyacceleration of said engine when the turbo-compressor discharge pressureis insufficient to maintain acceptable air/fuel ratios.
 4. Thecombination of claim 1 wherein said control means includes means for (1)maintaining said passage between 40% and 70% closed at engine idle andlow load-low speed conditions, (2) maintaining said passage fully closedat low speed-high load conditions and (3) maintaining said passage fullyopen at high speed-high load conditions.
 5. The combination of claim 4wherein said control means maintains said passage fully closed underheavy acceleration of said engine when the turbo-compressor dischargepressure is insufficient to maintain acceptable air/fuel ratios.
 6. Thecombination of claim 5 wherein said internal combustion engine is a twocycle compression-ignition engine having at least one piston cylinderand associated compression chamber,said engine having a compressionratio within the combustion chamber ranging from about 20:1 to about25:1.
 7. The combination of claim 6 wherein said blower includes asecond said bypass passage to thereby provide a pair of bypasspassages,said blower including a main housing rotatably supporting apair of mating impellers in an enclosed chamber having inlet and outletzones respectively connected with the compressor and the charge aircooler and the engine air intake, and further including an air inlethousing having a main air inlet portion leading directly into said inletzone and a pair of outlet ports, one each of said outlet ports leadingdirectly to a respective one of said bypass passages, a valve withineach said outlet port and affixed to a common actuating member, eachsaid valve being actuable from a position fully closing said outlet portto a position fully opening said outlet port.
 8. The combination ofclaim 7 wherein the geometric compression ratio within said combustionchamber is about 23:1.
 9. The combination of claim 1 wherein said blowerincludes a second said bypass passage to thereby provide a pair ofbypass passages,said blower including a main housing rotatablysupporting a pair of mating impellers in an enclosed chamber havinginlet and outlet zones respectively connected with the compressor andthe charge air cooler and the engine air intake, and further includingan air inlet housing having a main air inlet portion leading directlyinto said inlet zone and a pair of outlet ports, one each of said outletports leading directly to a respective one of said bypass passages, avalve within each said outlet port and affixed to a common actuatingmember, each said valve being actuable from a position fully closingsaid outlet port to a position fully opening said outlet port.
 10. Thecombination of claim 1 wherein said internal combustion engine is a twocycle compression-ignition engine having at least one piston cylinderand associated compression chamber,said engine having a geometriccompression ratio within the combustion chamber ranging from about 20:1to about 25:1.
 11. The combination of claim 10 wherein the geometriccompression ratio within said combustion chamber is about 23:1.
 12. Thecombination of claim 1 further comprising:a solenoid valve actuator forcontrolling said control valve means; means for generating an inputcontrol signal based on engine speed, boost air pressure as sensed atthe outlet of said turbo-compressor and operator demand; means forsupplying a feedback signal representing the actual angular position ofthe control valve means to the means for generating the input controlsignal.